The present invention generally relates to RF power amplifiers and, in particular, relates to efficient, linear RF signal amplification.
Several existing wireless communication standards are either in use, or planned for use in the near future. Current standards that enjoy varying degrees of deployment globally include the TIA/EIA-136 and Global Services for Mobile Communications (GSM) standards, which represent competing approaches for providing wireless communication and data services. The TIA/EIA-136 and GSM standards employ Time Division Multiple Access (TDMA) techniques. Other deployed standards, based on Code Division Multiple Access techniques, include the IS-95 standard. Newer standards, including those still in development, or enjoying initial roll out, include the so-called third generation (3G) standards. The 3G standards include the North American CDMA-based IS-2000, and the primarily European Wideband CDMA (WCDMA) standards. The Enhanced Data Rates for Global Evolution (EDGE) standards provide a migration path for TDMA and GSM networks towards 3G services.
Differing approaches to transmit signal modulation exist among the various standards, but each standard typically has specifications regarding transmit signal fidelity. The spectral requirements, such as spectral purity or adjacent channel power, impose certain performance requirements on the RF transmitters used within systems based on these standards. In some cases, the spectral requirements imposed by certain of these standards are quite rigorous. For example, the EDGE extensions to GSM and TDMA standards move away from the Gaussian Minimum Shift Keying in favor of 8-PSK modulation, which has significant amplitude modulation depth as well as strict spectral purity requirements. Such requirements place significant linearity demands on the associated transmitters.